The invention is directed to a rotatable cutting tool having a hard carbide insert affixed to a socket in an elongate body, and more specifically, to such a rotatable cutting tool designed so as to provide for a greater ease of manufacture, a more satisfactory braze joint between the hard carbide insert and elongate body, improved performance, and an indicator whereby the operator will know when the hard insert is worn and ready to be changed.
In the past, rotatable cutting tools have been put to a number of uses including use as a road planing tool in a road planing machine. Typically, a road planing machine includes a rotatable drum having a plurality of blocks affixed thereto. Each block contains a central bore therein. Earlier rotatable cutting tools used in road planing applications typically comprise an elongate steel body with a hard cemented carbide tip brazed into a socket contained in the forward end of the steel body. The steel body includes a reduced diameter portion adjacent the rearward end thereof. A retainer is positioned adjacent the reduced diameter portion of the steel body and functions to rotatably retain the rotatable cutting tool within the bore of the mounting block during operation. In operation, the drum rotates whereby the rotatable cutting tools impact the road surface so as to cut and break up the road surface.
Heretofore, a number of designs of rotatable cutting tools have been used or described in patents and/or printed publications.
U.S. Pat. No. 4,216,832 to Stephenson et al. discloses a rotary earthworking tool wherein FIG. 10 illustrates a hard cemented carbide insert. This insert includes a conical tip section, a frusto-conically shaped section axially rearward of the conical section, a cylindrical flange section axially rearward of the frusto-conically shaped section, and a valve seat contiguous with and positioned axially rearwardly of the cylindrical flange section. The valve seat consists of a second frusto-conically shaped section contiguous with and axially rearward of the cylindrical flange section and a cylindrically shaped boss contiguous with and axially rearward of the second frusto-conically shaped section. The assignee of the present patent application, Kennametal Inc. of Latrobe, Pa., has manufactured and sold rotatable cutting tools under the designation of C-3LR which utilize a cemented carbide insert having substantially the same configuration as the cemented carbide insert illustrated in FIG. 10 of U.S. Pat. No. 4,216,832 to Stephenson et al.
Kennametal Inc. has also manufactured various styles of rotatable cutting bits which utilize a cemented carbide insert wherein the insert includes the valve seat structure.
This style of a valve seat is generally shown in European Patent Application No. 84850079.9 published Oct. 24, 1984. It should be appreciated that cemented carbide inserts which utilize the valve seat structure require a meaningful amount of carbide to be positioned within the socket of the elongate steel body. The cemented carbide insert is a relatively expensive part of the overall rotatable cutting tool so that any reduction in the weight of the cemented insert without losing any performance properties would be desirable.
Even if the amount of carbide used in the cemented carbide insert remained the same, it would be highly desirable to provide an improved rotatable cutting tool utilizing a cemented carbide insert wherein more of the cemented carbide would be used to impact the substrate than which has been utilized in the past.
U.S. Pat. No. 4,497,520 to Ojanen shows a rotatable cutting bit which utilizes a so-called flat bottom hard carbide insert wherein the base section of this tip is positioned within a shallow flat bottom cylindrical bore contained in the front end of the elongate steel body.
Applicants are also aware of a carbide tip similar to the shape as set forth in U.S. Pat. No. 4,497,520, except that it contains a plurality of protrusions on the axially rearwardly facing flat bottom surface of the cemented carbide insert. The apparent purpose of these bumps is to maintain the uniformity of the braze thickness between the flat bottom of the insert and the flat bottom of the socket.
Applicants are also aware of the use of protrusions or bumps contained on the frusto-conically shaped surface of the valve seat of a cemented carbide insert. Again, the apparent purpose of these bumps is to maintain the uniformity of the braze thickness between the frusto-conically shaped surface of the valve seat and its corresponding surface of the socket.